The disclosure of Japanese Patent Application No. 2001-271860 filed on Sep. 7, 2001, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a valve driving apparatus for electromagnetically opening and closing a valve element functioning as an intake valve or exhaust valve of an internal combustion engine.
2. Description of Related Art
A valve driving apparatus for electromagnetically driving a valve element functioning as an intake valve or exhaust valve of an internal combustion engine has been known. For example, in a valve driving apparatus proposed in Japanese Patent Laid-Open Publication No. 10-280999, a plurality of electromagnetic actuators for driving a valve element is mounted to an actuator body. Moreover, wiring for distributing electric power to each electromagnetic actuator are also mounted to the actuator body. Each electromagnetic actuator includes an armature that is displaced integrally with a valve element, a pair of springs for biasing the armature to a neutral position, and a pair of electromagnets arranged in the direction in which the armature is displaced. When an exciting current is applied to an electromagnetic coil of the electromagnet, the armature is subjected to electromagnetic force toward the electromagnet. Accordingly, alternately applying an exciting current to the pair of electromagnets reciprocates the valve element, whereby each valve is opened or closed.
The above valve driving apparatus requires two wires for each electromagnet in order to distribute electric power to the electromagnetic coil of the electromagnet. Since each electromagnetic actuator uses a pair of electromagnets, four wires are required for each electromagnetic actuator. The valve driving apparatus therefore has an extremely large number of wires. For example, a four-cylinder internal combustion engine having four valves per cylinder would require sixty-four wires. Such a large number of wires require a large space. Moreover, a large connector is required to connect the wires to external drive circuitry.
One way to solve these problems is to reduce the thickness of the wires. However, a wire with a reduced cross-sectional area has an increased electric resistance (increased copper losses), thereby increasing the heating value. Therefore, the wires may overheat if a great amount of current is applied thereto. The reduced thickness of the wires enables a reduction in space for power distribution, but on the other hand causes overheating of the wires.
In view of the foregoing problems, it is an object of the invention to provide a valve driving apparatus of an internal combustion engine which enables a reduction in space for power distribution while minimizing overheating of the wires.
In order to achieve the foregoing object, in a valve driving apparatus of an internal combustion engine according to one aspect of the invention, a plurality of electromagnetic actuators for driving a valve element functioning as an intake valve or an exhaust valve of the internal combustion engine is mounted to an actuator body, and wiring for supplying electric power to each of the electromagnetic actuators is mounted to the actuator body. The actuator body has a flow path for allowing a cooling medium to flow therethrough. The wiring is provided near the flow path of the actuator body.
In the above valve driving apparatus, electric power is distributed to each electromagnetic actuator through the wiring mounted to the actuator body. As a result, each electromagnetic actuator is operated to drive a corresponding valve element, whereby the valve element functions as an intake valve or an exhaust valve. Heat generated by a current flowing through the wiring is partially transmitted to the actuator body and dissipated by the cooling medium flowing through the flow path. Since the wiring is provided near the flow path, most of the heat generated by the wiring is efficiently dissipated by the cooling medium. Although the use of thin wires generally increases the heating value, such improved heat dissipation suppresses overheating of the wires. Moreover, even if a large number of wires are required, the use of thin wires reduces the space required for them, and also reduces the size of connectors for connecting the wires to external drive circuitry. A reduction in space for power distribution is thus achieved while minimizing overheating of the wires.